Indesign epub to iTunes producer - ERROR ITMS-3000: "data_file" incomplete; missing required element "checksum" at XPath /package/book/assets/asset[2]/data_file"

Hi,

I have upgraded to the latest version on Indesign CC to use the wonderful new feature of publishing fixed layout epub 3.0's to upload in iBooks. Sadly, it doesn't seem to work. I have ironed out most errors on my file but the one code I cannot resolve is this: ERROR ITMS-3000: "Line 38 column 29: element "data_file" incomplete; missing required element "checksum" at XPath /package/book/assets/asset[2]/data_file"

From what I can tell, it is a mismatch in metadata. I have tried submitting the epub with no metadata entered in the indesign file, as well as with it added in. And I have filled all necessary fields in iTunes Producer, making sure they are a match. Still no luck.

I've spoken to Apple who advised me to remove the cover and screenshot files, as well as the epub from the iTP screen, and then add back in. This works for some people but not me. So now I am completely stuck with an ePub that's taken 2 weeks to build that I can't publish.

I have also ensured that file names are simple for screenshots and cover image, and are within recommended sizes (1400px cover on longest side, 1024x768 for screenshots). I have tried these as both png and jpegs.

Any help would be appreciated. It seems a common problem but rarely do I see a clear explanation for a resolution. Thanks.